Place a dishwasher-safe cup filled with plain white vinegar on the top rack of the dishwasher. Using the hottest water available, run the dishwasher through a cycle. The vinegar will help to wash away the loose, greasy grime, sanitizes, and helps remove the musty odor. Next, sprinkle a cupful of baking soda around the bottom of the tub and run it through a short cycle. The baking soda will help freshen and removing stains.
BEST soap scum remover!! This REALLY works well. After trying a few other Pinterest suggestions, I made this. It's odd, but it's GREAT. Make a vinegar "gel" by thickening vinegar with cornstarch. The vinegar CLINGS to what ever you spray it on...thus gives it more time to work. A little detergent cuts grease. I heated 1 cup of vinegar and 1 T corn starch in the microwave for 2 minutes. Add 2 T dish detergent and put it in a spay bottle. Spray. Wait 1hr. Wipe. Rinse.